> open -a Wine "/Applications/WinXP/drive_c/Program Files/WinMerge/WinMergeU.exe Z:\Users\usera Z:\Users\userb"
You don't need to use the open -a on the wine executable on MacOSX.
Also, you cannot use your WinXP directory to run programs from for
Wine. You need to install this program in the wine file structure.
Can you provide the command line you used to initalize Wine with?
If you mapped your Windows C: drive to be your Wine c: drive, you just
hosed up your Windows install and broke Wine.
The FAQ provides information on why not to do this and what you need
to do to recover from it.
James McKenzie